Mr Cameron told the BBC on Monday he would not seek a third term as prime minister at the 2020 election (assuming he wins a second term in May), saying that Home Secretary Theresa May, Chancellor George Osborne and Mr Johnson were in the frame to succeed him.

He said there would come a time when “a fresh pair of eyes and fresh leadership would be good”.

Mrs May had nothing to say to the waiting media when she arrived for cabinet this morning, and Mr Osborne has not spoken yet, but Mr Johnson embarked on a series of interviews and played down his prospects.

He told LBC: “The next leader of the Tory party is probably a babe unborn. Kids grow up fast these days, folks.”

‘Decapitated by flying frisbee’

Outside the radio studios, he went further, saying: “It is not going to happen. It is more likely that I will be reincarnated as an olive or locked in a disused fridge, decapitated by flying frisbee.

“It is vanishingly unlikely and what is going to happen, I hope very much, is that the prime minister will be returned with a thumping majority and deliver his mandate for five years.”

Mr Cameron’s comments were criticised by shadow chancellor Ed Balls, who called him “spectacularly self-indulgent, presumptuous and arrogant” for giving the impression he would win the general election on 7 May.

On Monday, former Downing Street director of communications Alastair Campbell told Channel 4 News (watch video above) that his seemingly off-the-cuff remark was “a bit of a disaster” for the Tories, who could find their election campaign dominated by speculation over a future leader.

But Defence Secretary Michael Fallon told BBC Radio 4’s Today programme Mr Cameron was just giving a “fairly straight answer” to a question and was making it clear he was “not going to go on and on”.

‘Statement of the bleeding obvious’

Speaking to BBC Newsnight, Michael Gove, who has also been mentioned as a future Tory leader, said it was “a statement of the bleeding obvious” and showed him to be “a normal, sane, decent guy who is in politics for the right reasons”.

The bookmaker Paddy Power puts Mr Johnson in the lead to succeed Mr Cameron, with odds of 2/1. Theresa May is next on 7/2, with George Osborne on 8/1 and Michael Gove on 10/1.

Ladbrokes also puts London’s mayor in the lead (5/2). Next are the home secretary (4/1), the chancellor (7/1) and Culture Secretary Sajid Javid (10/1).